Method for sealing an enclosure for an electronic component

ABSTRACT

A method for sealing an enclosure for an electronic component, the enclosure including a base having on one face a composite glass layer, and a cap having a face to be joined with the base which is free from any glass layer. The method includes heating the cap to raise the temperature of its glass-free face to a temperature greater than the softening point of the glass layer on the base, and joining the heated glass-free face of the cap with the glassed face of the base, thereby softening the glass layer of the base, and cooling the joined cap and base to form a seal between them at the interface of the joined faces.

United States Patent 1 Rogers I 3,768,991 (451 Oct. 30, 1973 [54] METHODFOR SEALING AN ENCLOSURE 3,346,357 lO/l967 Baak 65/36 X FOR ANELECTRONIC COMPONENT [75] Inventor: Bryant C. Rogers, La Jolla, Calif.Primary Exami"e' Rbert Lindsay AttorneyRoger S. Borovoy [73] Assignee:Dlacon, Inc., San Diego, Calif. 221 Filed: June 14, 1912 57 ABSTRACT[21] Appl. No.: 262,798 A method for sealing an enclosure for anelectronic component, the enclosure including a base having on 52 Us ClU one face a composite glass layer, and a cap having a 1 65/36 29/582 3face to be joined with the base which is free from any [51] Int- Cl C03c27/02 1 glass layer. The method includes heating the cap to [58] FieldI36 42 raise the temperature of its glass-free face to a temper- 581ature greater than the softening point of the glass layer 7 on the base,and joining the heated glass-free face of [56] Reterences Cited the capwith the glassed face of the base, thereby soft- UNITED S T ening theglass layer of the base, and cooling the TA ES PATENTS joined cap andbase to form a seal between them at 2,512,971 6/1950 Roovers 65/36 X thi t fa of the joined faces, 3,281,606 10/1966 Lueck 65/59 X 3,312,5404/1967 Plumbo et al 65/59 4 Claims, 2 Drawing Figures T0 VACUUM T0 POWERL/TO VACUUM SUPPLY SUPPLY SUPPLY {AZ 22 2 445, 50- NON-DEVITRIFIED ll Al7 3 GLASS? l l W /|Z /f'/f /i',-,

l l DEVITRIFIED mm 2? BACKGROUND OF THE INVENTION 1. Field of theInvention This invention generally relates to the field of sealingpackages, normally glassed ceramic packages, to form hermetic enclosuresfor semiconductor devices.

2. Prior Art According to prior practice, exemplified by U.S. Pat. No.3,404,213, the cap and a base for a semiconductor package to be sealedtogether both have a glass layer on one surface. The two glass layersare then placed adjacent each other and the entire structure heateduntil the glass layers soften and fuse together to form a glass seal.

One disadvantage of the sealing techniques of the prior art is that aglass layer is required both on the cap and on the base. Not only is anextra glazing operation required for the cap, but, once glazed, thesecaps are not storable for any length of time at elevated temperatures.Secondly, during sealing, it is necessary to heat the base, includingthe delicate semiconductor device to be enclosed, to a temperaturesufficient to soften the glass of the base, thereby, in many instances,doing damage to the electrical properties of the device.

SUMMARY OF THE INVENTION Briefly, the method of this invention forsealing an enclosure for an electronic component, the enclosureincluding a base having on one face a composite glass layer having afirst lower portion which is substantially devitrified and a secondupper portion which is substantially non-devitrified, and a cap havingthe face to be joined to the base free from any glass layer, includesthe following steps: (1) heating the cap to raise the temperature of itsglass-free face to a temperature greater than the softening point of theglass layer on the base; (2) joining the heated glass-free face of thecap with the glassed face of the base, thereby softening the glass layeron the face of the base; and (3) cooling the joined cap, and base,thereby forming a seal between the cap and the base at the interfacebetween the joined faces. Preferably, the method of the invention alsoincludes the additional step of heating the base to raise thetemperature of the glass layer to a temperature below its softeningpoint prior to joining the cap to the base.

Since the cap does not require any glass layer, and must remainglass-free, the cap-glazing operation required in the prior art has beeneliminated. These unglazed caps may be stored at elevated temperatureswithout any deleterious effect contrary to what was possible using priorart sealing techniques such as described in U.S. Pat. No. 3,404,213.And, since the base is heated to -a temperature lower than the softeningpoint of the glass, damage to the semiconductor device is minimized oreliminated. Finally, the equipment required for the technique of theinvention is much simpler, more compact, less costly, and more easilyemployed in clean-room conditions than the larger, more expensiveconventional belt furnaces of the prior art.

The specifics of the sealing technique of the invention will be moreclearly understood from the more detailed description which follows:

DESCRIPTION OF THE FIGURES FIG. 1 shows theapparatus' used in the methodof the invention to hold and to heat the cap and base during the sealingoperation of the invention;

FIG. 2 shows the package after it has been sealed in accordance with themethod of the invention.

DETAILED DESCRIPTION OF THE INVENTION The sealing operation of' theinvention employsa base 10 and a cap 11. The base 10 is normally aceramic material conventionally employed in the semiconductor industry.A conductive lead frame 12 is firmly attached to the base 10, beingembedded in a composite glass layer comprising layers 13 and 14. Thefirst lower portion 13 is substantially devitrified. The second upperportion 14 is substantially non-devitrified both devitrified andnon-devitrified glass layers are well known in the art, and aredescribed in U.S. Pat. Nos. 3,258,350 and 3,697,666. The lead frame 12has surfaces, as shown in FIG. 1, exposed for electrical contact bothwithin and without the perimeter of base 10, the intermediate part ofthe lead frame between the exposed portions being embedded in thecomposite glass layerl3, l4. Semiconductor device 15 is attached to base10 within cavity 16. Wires l7 and 18 are used to interconnect the activeportions of the semiconductor device 15 with the metal conductive leadsl2.

Cap 11, shown in FIG. 1, has a glass-free face 19. It is this glass-freeface 19 which will be sealed to glass layer 13, 14 on base 10.

In the method of the invention, the cap 11 is heated, using heater block20, to a temperature greater than the softening point of the glass layer14 on the face of base 10. Heater block 20 is heated using coils 21which are connected through leads 22 and 23 to a conven tional powersupply. To hold cap 11 within the block 20, conventional vacuumtechniques are employed, using vacuum lines 24 and 25 which areconnected to a conventional vacuum supply.

In a preferred embodiment of the invention, base 10 is also heated. Base10 is mounted in a separate heating block 26 which is heated by coil 27connected through leads 28 and 29 to a power supply. Base 10, whichrests I in block 26, is heated sufficiently so that the glass layeringly, it is essential to the invention that the glass layer 13, 14remains at a temperature below its softening point up until the timewhen it is contacted by heated c p In accordance with the invention, asexplained above, after the heating has been completed, cap 11 and base10 are contacted together. Heating block 20 is supported on rods 30 and31 so that the heating block and the cap, held by the vacuum in lines 24and 25, may be lowered into the position where face 19 of cap 11contacts the glass layer 14 of base 10. Many techniques may be used forthe movement of block 20, the one shown being merely illustrative.

The heat conducted from block 20 through cap 11 and through face 19serves to soften the glass of glass layer 14, thereby effecting the sealbetween the two parts of the package upon contact.

After the sealing operation has been completed, the vacuum isdisconnected from tubes 24 and 25, thereby releasing cap 11 from block20. Heater block is then raised so that the sealed package may beremoved from the lower heater block 26. At that time a new cap isinserted into heater block 20, the vacuum supply is again connectedthrough lines 24 and 25 to hold the new cap, and a new base is insertedinto lower heater block 26. The equipment is then ready for repetitionof the sealing operation.

The final package, sealed in accordance with the method of thisinvention, is shown in FIG. 2. The parts are numbered exactly as in FIG.1, for ease of comparison.

What is claimed is:

1. A method for sealing an enclosure for an electronic component, saidenclosure including a base having on one face a composite glass layerhaving a first lower portion which is substantially devitrified and asecond upper portion which is substantially nondevitrified, and a caphaving a face to be joined to said base which is free from any glasslayer, the method comprising:

heating said cap to raise the temperature of said glass-free face to atemperature greater than the softening point of said glass layer;joining said heated glass-free face of said cap with th glassed face ofsaid base, thereby softening the glass layer of the base; and coolingthe joined cap and base, thereby forming a seal between the cap and baseat the interface between the joined faces. 7

2. The method of claim 1 further characterized by the additional step ofheating said base to raise the temperature of said glass layer to atemperature below its softening point prior to joining the cap to thebase.

3. The method of claim 1 further characterized by the heating of saidcap being accomplished by applying a heated, heat-conductive member tothe face of said cap opposite from the face to be joined to said base,and conducting the heat from said member through the cap to heat theface to be joined to said base.

4. The method of claim 2 further characterized by the heating of saidbase being accomplished by applying a heated, heat-conductive member tothe face of said base opposite from said glassed face, and conductingthe heat from said member through the base to heat said glassed face.

t II

1. A method for sealing an enclosure for an electronic component, saidenclosure including a base having on one face a composite glass layerhaving a first lower portion which is substantially devitrified and asecond upper portion which is substantially non-devitrified, and a caphaving a face to be joined to said base which is free from any glasslayer, the method comprising: heating said cap to raise the temperatureof said glass-free face to a temperature greater than the softeningpoint of said glass layer; joining said heated glass-free face of saidcap with the glassed face of said base, thereby softening the glasslayer of the base; and cooling the joined cap and base, thereby forminga seal between the cap and base at the interface between the joinedfaces.
 2. The method of claim 1 further characterized by the additionalstep of heating said base to raise the temperature of said glass layerto a temperature below its softening point prior to joining the cap tothe base.
 3. The method of claim 1 further characterized by the heatingof said cap being accomplished by applying a heated, heat-conductivemember to the face of said cap opposite from the face to be joined tosaid base, and conducting the heat from said member through the cap toheat the face to be joined to said base.
 4. The method of claim 2further characterized by the heating of said base being accomplished byapplying a heated, heat-conductive member to the face of said baseopposite from said glassed face, and conducting the heat from saidmember through the base to heat said glassed face.